In a number of mechanical applications involving the movement of a shaft relative to a fixed work piece, friction between the shaft and the workpiece results in premature wear of one or both parts with consequent formation of filings which cause additional wear, and generation of heat. To extend the working life of the shaft and the work piece, it is desirable to minimize the surface wear on the work piece and the shaft. It is known to decrease the wear and friction by use of an appropriate lubricant applied to the contacting surfaces. However, the lubricant must be periodically replenished. Further, the lubricant does not provide support to the shaft as it moves relative to the work piece, increasing the prospect of wear with formation of filings.
For reducing friction between a moving shaft and a workpiece and for providing support for the shaft it is known to use a bearing which surrounds the moving shaft and fits inside the bore of the workpiece. Though various bearings can be used, of particular importance is a bearing produced from a polymeric material which can be fit into the bore of the workpiece to surround the shaft and thereby minimize frictional contact between the shaft and the workpiece.
A bearing of this type must be adjustable in diameter to allow insertion into the workpiece bore, as well as to accommodate slight variations in the diameter of the shaft and the bore. Further, the bearing must be formed so that it does not work its way out of the bore in the workpiece during operation. Typically, flanges are provided at the edges of the bearing to resist longitudinal movement of the bearing from the workpiece bore.
It is known to employ bearings in sheet metal to reduce the friction of a shaft inserted through a bore in the sheet metal. A bearing of this type is manufactured by Thomson Industries, Inc., Port Washington, N.Y., and Performance Plastics, Incorporated, Cincinnati, Ohio. The bearing is comprised of a cylindrical side wall having a gap cut therein, a small flange on one end of the side wall, and a large flange located on the opposite end of the side wall. After the small flange has been fit into the sheet metal workpiece bore, and a shaft inserted inside the cylindrical bearing wall, the rotating, oscillating or linearly moving shaft will deposit debris into the gap of the bearing, keeping the shaft surface relatively clean. If the movement of the shaft is rotational or oscillatory, the bearing will typically rotate with the shaft because there is no means at the bearing-bore interface for preventing rotation of the bearing inside the sheet metal bore.
In a modification of this standard type of sheet metal bearing, Performance Plastics, Inc. developed a pop-in bearing which has a sidewall, a top edge with two outward extending lips thereon and a bottom edge with a wide flange, albeit having notches therein. This type of bearing was designed for sheet metal applications where the bore is created by stamping a nearly circular hole, leaving a small tab extending into the aperture. This tab is bent away from the aperture, creating a projection which mates with one of the notches in the wide flange of the bearing. As before, the sidewall has a gap to allow the bearing to be used in bores having slightly differing diameters. This pop-in bearing is restrained from rotating with the shaft by the mating of the sheet metal tab with the bearing flange notch. The outward projecting lip on the upper edge of the bearing restricts longitudinal movement of the bearing in the sheet metal workpiece bore.
Though the above bearings are useful in the applications where the workpiece is of relatively narrow thickness, such as with sheet metal, the bearings are not as useful in thicker workpiece applications. As the workpiece thickness increases the bearing sidewall length therefore must also increase, rendering the bearing more flexible and thus more likely to work out of the bore of the workpiece. If the bearing sidewall is stiffened to counteract this tendency, it becomes difficult to insert the bearing into the workpiece.